Method for transmitting data between a base station and a transponder

ABSTRACT

In known methods for the transmission of data, the data transmission rate is reduced by bit errors especially at high carrier frequencies. In the new method, the data transmission rate can be significantly increased due to the increased reliability in the data transmission by means of the integration of a test signal.

FIELD OF THE INVENTION

The present invention relates to a method for the transmission of databetween a base station and a transponder by a modulated electromagneticwave.

BACKGROUND INFORMATION

Such a method is known from the publication DE 101 38 217.0. Therein,information packets are transmitted between a base station and atransponder. The information packets consist of a header section and amiddle section with a data region. In the middle section, the data ofthe data region are encoded with the identifications allocated to thelogic values of the information symbols in the header section. Adisadvantage of the method is that disturbing or noisy interferencesreduce the reliability of the data transmission in the communication dueto reflections and/or absorptions when utilized in the range of UHF andhigher. For the correction of the read errors, the entire data packetmust be transmitted.

A further method is known from the publication EP 473,569 B1. Therein,digital data are exchanged between a base station and a passivetransponder by means of an amplitude modulated carrier wave. Theindividual bits of a data word consist of a time span or interval inwhich the electromagnetic field is switched on and a time span orinterval in which the electromagnetic field (field gap or notch) isswitched off, whereby the field gap serves as a separator between twosuccessive bits. The logic value of the bits is determined by the lengthof the time in which the electromagnetic field is switched on. The fixedtime amount of the field gap is summed or additionally counted for thetotal time for the representation of the individual bits. Furthermore,in the passive system, the energy for the transponder is acquired out ofthe carrier field by means of absorption modulation.

A further method is known from the publication EP 0,777,191 A1. Therein,data are transmitted by means of a PWM modulated carrier wave, wherebythe logic values of the bits are represented by various different timelengths, and the carrier field is briefly switched on for the separationof the individual bits at the end of a time interval in the so-calledforward link. Furthermore, various different encoding methods for thetransmission of digital data are known from Finkenzeller, “RFIDHandbuch” (“RFID Handbook”), especially page 106 et seq. and thepublication U.S. Pat. No. 3,560,947.

Due to the increasing security or safety demands, a plurality ofinformation packets must be modulated onto a carrier wave inever-shorter time spans or intervals. Preferably an amplitude modulation(ASK) is used for the modulation. In order to achieve a higher datatransmission rate and a higher transmission distance or range, carrierfrequencies in the range of UHF and microwaves are being increasinglyutilized in the field of the transponders. The basic foundation of thebi-directional data transmission between transponder and base station isformed by a data protocol, which, among other things, sets or fixes thenumber of the information symbols, such as for example the logic valuesper data bit, and also defines the identification of the individualsymbols. Especially in the UHF range, read errors arise in the datatransmission due to change or variation of the transmission conditionsas a result of reflections and the constructive and destructiveinterferences associated therewith. Because this results in a repeatedtransmission of the data word, the effective data transmission rate isconsiderably reduced.

A disadvantage of the previous methods is that the effective datatransmission rate is reduced due to the transmission errors especiallyin the range of very high frequencies due to the fluctuatingtransmission conditions. This reduction of the data transmission rate isnoticeable in a disturbing or interfering manner in time-criticalapplications. It is an object of the present invention to set forth amethod for the transmission of data, which increases the reliability ofthe data transmission and can be carried out in a simple and economicalmanner.

SUMMARY OF THE INVENTION

This object is achieved according to the invention in a method for thetransmission of data between a base station and a transponder by meansof an electromagnetic wave, in which an information packet is modulatedonto this electromagnetic wave, which information packet comprises adata section with a data word and that is embodied as a sequence ofbits, to the logic value of which a modulation state is respectivelyallocated, whereby respectively one bit of the bit sequence istransmitted in the time interval generated by means of one of twosuccessive clock pulses, characterized in that in addition to the clockpulses, a test signal for the testing of the transmitted logic value istransmitted with a prescribed time duration, during the time interval,and a time constant modulation state is allocated to the test signal.

The above object is further achieved according to the invention in amodulation control arrangement for carrying out the inventive method,comprising a sample/hold unit in which is stored a first voltage valuethat is proportional to the time duration of the test signal, anintegration unit that provides a second voltage value proportional tothe duration of a charging current of a constant current source, acomparator for the comparison of the first voltage value with the secondvoltage value, a modulation control unit for generating the modulationstate of the electromagnetic wave dependent on an output signal of thecomparator and the bit sequence of the data word and for resetting theintegration unit.

The above object is still further achieved according to the invention ina modulation control arrangement for carrying out the inventive method,comprising a memory unit, in which a time point determined by theduration of the test signal is stored, a multiplexer that switchesbetween time points that are allocated to the logic values of the bitsthat are to be transmitted and the time point allocated to the durationof the time interval and outputs the time point, a counter unit thatprovides a time point proportional value, a comparator for comparing thevalue of the multiplexer and the value of the counter, and a modulationcontrol unit for generating the modulation state of the electromagneticwave dependent on an output signal of the comparator and the bitsequence of the data word.

Accordingly, the essence of the invention consists in that thereliability is increased in connection with an additional test signal ina transmission. For this purpose, information packets are modulated ontoan electromagnetic wave by a base station and a transponder. Theinformation packet comprises a data section with a data word, wherebythe data word is embodied as a sequence of bits, to the logic value ofwhich a modulation state is respectively allocated, and in whichrespectively one bit of the bit sequence is transmitted by means of atime interval generated from two successive timing or clock pulses.Moreover, during the time interval, a test signal with a prescribed timeduration is generated, and a time-constant modulation state is allocatedto the test signal. In this regard, investigations of the applicant haveshown that it is advantageous to insert the test signal at the beginningof a time interval.

It is an advantage of the method that, by means of the insertion of thetest signal, independently of the modulation method, a prescribedmodulation state is given, which can be used as a reference point forthe determination of the logic value of the bit. Thereby, the durationof the test signal is given and can be communicated to the receiver inthe header section of the respective information packet. A furtheradvantage is that the duration of the test signal is independent of thelength of the time interval.

In a further embodiment of the method, for the decoding of the receivedbit sequence, the logic value of the bit transmitted in th etimeinterval is derived from its modulation state in a time point determinedby the duration of the test signal. Further it is advantageous toallocate a prescribed modulation state to the test signal during thetransmission of a data section. Thereby, the detection of the modulationstate during an entire time interval by means of integration methods isomitted. Since the likelihood of the detection of a bit error,especially in the range of UHF, through an undesired change of themodulation state as a result of reflections is substantially reduced,the reliability of the data transmission and the effective datatransmission rate are substantially increased. Furthermore, bit errorscan be recognized and immediately corrected, already during thetransmission of the respective time interval, from the modulation statethat is prescribed at a predetermined time point. The correction ischecked after the completion of the transmission of the data word bymeans of one or more test bits (CRC region). Investigations of theapplicant have shown that a substantial increase of the effective datatransmission rate is achieved hereby.

Furthermore, other investigations of the applicant have shown that thecontrol of the modulation state in connection with the transmission of atest signal in the header section can be carried out in a simple mannerby means of a so-called “peek detector”, and the current consumption canbe reduced through the saving or avoiding of a complicated and costlytime measuring unit. Thereby, the communication distance or range isincreased especially for passive transponders.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive apparatus shall be explained in the following on the basisof the example embodiments in connection with several schematicdrawings. It is shown by:

FIG. 1 a a first timing or clock signal for a data transmission, and

FIG. 1 b a time-limited test signal, and

FIG. 1 c a bit sequence of a data word that has been transmitted, and

FIG. 1 d the time course of the modulation state, and

FIG. 2 a a second timing or clock signal, and

FIG. 2 b a test signal, and

FIG. 2 c a bit sequence of a data word that is to be transmitted, and

FIG. 2 d a modulation signal, and

FIG. 3 a first arrangement or apparatus for the control of the timecourse of the modulation state, and

FIG. 4 a second apparatus or arrangement for the control of the timecourse of the modulation state.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS OF THE INVENTION

With reference to the time courses of the signals illustrated in theFIGS. 1 a–1 d or 2 a–d, the relationship between a test signal RFM and adata signal L2S in a sychronous data transmission is explained, as it isneeded for the generation of the time variation or change of themodulation of an electromagnetic wave. In this context, for example, amodulated electromagnetic wave is transmitted from a base station, fromwhich electromagnetic wave a timing or clock signal CLK is extracted ina transponder. Subsequently, the electromagnetic wave of the basestation is modulated in the transponder. For this purpose, especially athigh frequencies for example in the range of UHF, the reflected wave ismodulated through a phase and/or amplitude modulation by means of amodulation control unit. In this context, in the FIGS. 1 a–1 d theintroduction of the test signal is shown in connection with a staticmodulation method, in the FIGS. 2 a–2 d the integration of the testsignal is shown with a dynamic modulation method, whereby no fixedallocations to a modulation state are prescribed for the logical one andof the logical zero. Rather, the two logic values define themselves astime points relative to the duration of the time interval Ty or from asequence of modulation variations or changes that occur at certain timepoints.

In the following, the FIGS. 1 a to 1 d are explained. In the FIG. 1 a,the course of a timing or clock signal CLK is illustrated. In thisregard the time course of the voltage of the individual clock pulses isillustrated, whereby respectively two successive voltage pulses define atime interval Tx. Furthermore, the course of the test signal RFM isillustrated in the FIG. 1 b. It respectively begins with each clocksignal CLK and ends after a given time T1. While the signal RFM isapplied or prevails, it comprises a constant value. A bit sequence L2Sthat is to be transmitted is illustrated as a part of a data word in theFIG. 1 c. In this regard, the modulation state during the time intervalTx is applied as a high level for a logic one and as a low level for alogic zero. The course of the modulation state is illustrated in theFIG. 1 d. In this regard, during the time duration T1, a high level isprescribed by the test signal at the beginning of each time interval.Thereafter, the modulation state changes at the time point z1 only whena logic zero is transmitted next thereafter. At the end of the intervalTx, the modulation state changes from low to high insofar as a logiczero was transmitted.

An advantage of the invention is that, through the test signal, thelogic value of the respective transmitted bit is extracted in thereceiver through detection of the modulation change and of themodulation state at the time point Z1. If a different change of themodulation state other than from high to low exists at the time pointZ1, then a bit error is determined and immediately corrected, that is tosay the detected logic state one is corrected to a logic state zero.

In the following, the FIGS. 2 a–2 d are explained. In the FIG. 2 a, thetime course of the timing or clock signal CLK1 is illustrated. In thisregard, a time interval Ty is defined from respectively two successivetiming or clock signals CLK1. In the FIG. 2 b, the time course of a testsignal RFM1 is illustrated. It respectively begins anew with each clocksignal CLK 1 and ends after a prescribed time T2. The value of the testsignal RFM1 changes from high to low at the time point Z2. A bitsequence L2S1 that is to be transmitted is shown as part of a data wordin the FIG. 2 c, whereby a high level is allocated to a logic one duringthe entire time interval Ty and a low level is allocated for logic zero.

The course or progression of the modulation state resulting from theFIGS. 2 a–2 c is illustrated in the FIG. 2 d: in the present example ofa dynamic modulation method, the time point Z3, that is to say onequarter of the time interval Ty, is allocated to the logic one, and thetime point Z4, that is to say one half of the time interval Ty, isallocated to the logic zero. Insofar as the modulation state was lowbefore the first illustrated time interval, it changes to the modulationstate high at the beginning of the first illustrated time interval untilthe time point Z2. Thereafter, the modulation state changes at the timepoint Z3 because a logic one is transmitted. At the end of the firsttime interval, the modulation state changes. In the second timeinterval, the modulation state changes at the time point Z21 and at thetime point Z41 because a logic zero is transmitted. In this regard itbecomes clear that the logic value of the bit that is to be transmittedis given from the change of the modulation state at defined time points.Through the introduction of the test signal RFM, an additionalinformation is provided, that can be used for the testing whether anundesired modulation state change is present. Hereby a bit error can bedetected with high reliability and, if applicable, corrected, within therespective time interval Ty.

FIG. 3 shows an apparatus for the integration of a test signal to eachbit of a bit sequence of a data word. For this purpose, a value of acharge voltage of a capacitance with a known time constant is allocatedto the time length of the test signal. In this regard, the charge timeconstant of the capacitance to be charged, for example arranged in atransponder, is known in the transmitter, for example a base station. Inorder to notify the transponder of the time length of the test signalthat is to be integrated in its reply signal, a voltage value HPallocated to the time length of the test signal is transmitted by thebase station in the header section of an information packet. In thetransponder, the voltage value HP is stored in a sample/hold or memoryunit SH. From the memory unit SH, the voltage value HP is provided to acomparator COMP. Simultaneously, the charge voltage HPC is applied tothe comparator COMP. The charge voltage HPC is advantageously increasedproportional to time by a current source IQ. If the voltage value HPCexceeds the voltage value HP, this is reported or communicated to acontrol unit MODGON by the comparator by means of an output OUT bychanging a voltage level prevailing at the output OUT. Moreover, a resetinput POR, a data input L2S, which provides the bit sequence of the dataword that is to be sent, a system clock input TAKT and a data clockinput CLK are connected to the control unit MODCON, which determines thetime course or progression of the modulation states of the reply signalby means of an output RMOD. Furthermore, the discharging time point ofthe capacitance RC is controlled by the control unit MODCON by means ofan output DCLK. Through the output DCLK, in this regard, the capacitanceRC is discharged dependent on the time points derived from the dataclock CLK extracted out of the received wave of the base station.Hereby, the level at the output OUT of the comparator COMP varies.

It is an advantage of the apparatus or arrangement that the length ofthe test signal can be changed in a simple manner through the height ormagnitude of a value, and that the test signal can be integrated into anexisting control unit in a current-saving manner through the small orlow required additional circuit effort, complexity or expense.

A further apparatus or arrangement for the integration of a test signalto each bit of a bit sequence of a data word is illustrated in the FIG.4. In the explanation of the drawings, only the differences relative tothe embodiment of the FIG. 3 are represented. The time length of thetest signal HPD extracted out of the header section of the informationpacket is stored as a value in the storage or memory unit TREF. Thevalue is provided to a multiplexer MUX. Furthermore, the multiplexerreceives a signal SELAB delivered from the control unit MODCON. Thevalues of the signal SELAB are generated by the control unitcorresponding to the logic values of the bits, in that a time point isallocated to each logic value, whereby this time point is determined bya fractional portion of the length of the time interval defined betweentwo successive data clock pulses CLK. The multiplexer makes the valuesHM, ordered according to their size or magnitude, available to thecomparator COMP. Simultaneously the value HD of a counter unit COUNT isapplied to the comparator. In this regard, the counter is counted-up bymeans of an oscillator OSC and reset by means of the signal DCLK witheach data clock signal CLK. If the value HD exceeds the value HM, thevoltage level at the output of the comparator COMP changes.

It is an advantage of the apparatuses, that by these apparatuses, in asimple manner, a test signal can be integrated into a data transmissionindependent of the respective modulation method. Thereby, the effectivedata transmission rate is considerably increased. Moreover, both controlapparatus can be carried out or embodied in a very current-savingmanner.

1. A method for the transmission of data between a base station (BS) anda transponder (TR) by means of an electromagnetic wave, in which aninformation packet (IP) is modulated onto this electromagnetic wave,which information packet comprises a data section (DA) with a data wordand that is embodied as a sequence of bits, to the logic value of whicha modulation state is respectively allocated, whereby respectively onebit of the bit sequence is transmitted in the time interval (TX)generated by means of one of two successive clock pulses, characterizedin that in addition to the clock pulses, a test signal (RFM) for thetesting of the transmitted logic value is transmitted with a prescribedtime duration (T1), during the time interval (TX), and a time constantmodulation state is allocated to the test signal (RFM).
 2. The methodaccording to claim 1, characterized in that the test signal (RFM) isinserted at the beginning of a time interval (TX).
 3. The methodaccording to claim 1, characterized in that the logic value of the bittransmitted in the time interval (TX) is derived from the change of themodulation state in a time point determined by the duration of the testsignal (RFM).
 4. The method according to claim 1, further comprisingrecognizing and correcting bit errors during the transmission of thedata word.
 5. A modulation control arrangement for carrying out themethod according to claim 1, comprising a sample/hold unit (SH) in whichis stored a first voltage value proportional to the time duration of thetest signal (RFM), an integration unit (RC) that provides a secondvoltage value proportional to the duration of a charging current of aconstant current source (IQ), a comparator (COMP) for comparing thefirst voltage value with the second voltage value, a modulation controlunit (MOD_CON) for generating the modulation state of theelectromagnetic wave dependent on an output signal (OUT) of thecomparator (COMP) and the bit sequence of the data word (L2S) and forresetting the integration unit (RC).
 6. A modulation control arrangementfor carrying out the method according to claim 1, comprising a memoryunit (TREF), in which a time point determined by the duration of thetest signal (RFM) is stored, a multiplexer (MUX) that switches betweentime points that are allocated to the logic values of the bits that areto be transmitted and the time point allocated to the duration of thetime interval (TX) and outputs the time point, a counter unit (COUNT)that provides a time point proportional value, a comparator (COMP) forcomparing the value of the multiplexer (MUX) and the value of thecounter (COUNT), and a modulation control unit for generating themodulation state of the electromagnetic wave dependent on an outputsignal (OUT) of the comparator (COMP) and the bit sequence of the dataword (L2S).
 7. The method according to claim 1, characterized in that,for the decoding of the received bit sequence, the logic value of thebit transmitted in the time interval (TX) is derived from its modulationstate in a time point determined by the duration of the test signal(RFM).
 8. The method according to claim 1, characterized in that apredetermined modulation state is allocated to the test signal (RFM)during the transmission of a data section.
 9. A method of transmittingdata between a base station and a transponder via an electromagneticwave, comprising the steps: a) providing successive clock pulses thatdefine successive time intervals extending respectively from one to anext of said clock pulses; b) providing a test signal includingsuccessive test signal pulses each respectively having a prescribed timeduration during a respective time interval of said successive timeintervals, wherein each said test signal pulse has a time constantmodulation state during said prescribed time duration thereof; c)providing a bit sequence of bits that form an information packetincluding a data section with a data word made up of a succession ofsaid bits, wherein said bits respectively represent logic values andwherein each one of said logic values has a respective modulation stateallocated thereto; d) generating a modulation signal dependent on andresponsive to said clock pulses, said test signal, and said bitsequence; and e) modulating said modulation signal onto saidelectromagnetic wave to produce a modulated electromagnetic wave, andtransmitting said modulated electromagnetic wave, such that a respectiveone of said test signal pulses and a respective one of said bits havinga respective one of said logic values is transmitted during eachrespective one of said time intervals.
 10. The method according to claim9, wherein each one of said test signal pulses commences at a beginningof a respective one of said time intervals.
 11. The method according toclaim 9, further comprising receiving and decoding said modulatedelectromagnetic wave, and using said test signal pulses in said decodingto test accuracy of said logic values as transmitted in said modulatedelectromagnetic wave.
 12. The method according to claim 9, furthercomprising receiving said modulated electromagnetic wave, and decodingsaid bit sequence from said modulated electromagnetic wave bydetermining said logic value of a respective one of said bits from arespective modulation state of said modulated electromagnetic wave at atime point determined by said prescribed time duration of said testsignal pulse in the one of said time intervals during which saidrespective bit is transmitted.
 13. The method according to claim 9,further comprising receiving said modulated electromagnetic wave, anddecoding said bit sequence from said modulated electromagnetic wave bydetermining said logic value of a respective one of said bits from arespective change of a modulation state of said modulatedelectromagnetic wave at a time point determined by said prescribed timeduration of said test signal pulse in the one of said time intervalsduring which said respective bit is transmitted.
 14. The methodaccording to claim 9, wherein said information packet further comprisesa header section in which said prescribed time duration of said testsignal pulses is defined.
 15. The method according to claim 9, whereinsaid prescribed time duration is independent of and shorter than saidtime interval.
 16. The method according to claim 9, wherein said timeconstant modulation state is a predetermined modulation state that isallocated to said test signal pulses of said test signal duringtransmitting of said data section.
 17. The method according to claim 9,further comprising a step of recognizing and correcting a bit errorduring transmitting of said data word.
 18. A modulation controlarrangement for generating a modulated electromagnetic wave dependent onand responsive to a clock signal, a test signal and a bit sequence, saidarrangement comprising: a sample/hold unit adapted to store a firstvoltage value proportional to a prescribed time duration of a testsignal pulse of said test signal; a constant current source having anoutput adapted to provide a charging current; an integration unit havingan input connected to said output of said constant current source, andhaving an output adapted to provide a second voltage value proportionalto a duration of said charging current of said constant current source;a comparator having a comparator output, a first input connected to anoutput of said sample/hold unit, and a second input connected to saidoutput of said integration unit, wherein said comparator is adapted tocompare the first voltage value with the second voltage value and toproduce a comparator output signal responsive thereto at said comparatoroutput of said comparator; and a modulation control unit having a firstinput connected to said comparator output of said comparator, a secondinput adapted to receive the clock signal, a third input adapted toreceive the bit sequence, a reset output connected and adapted toprovide a reset signal to a reset input of said integration unit, and amodulation signal output adapted to provide a modulation signaldependent on said comparator output signal and said bit sequence.
 19. Amodulation control arrangement for generating a modulatedelectromagnetic wave dependent on and responsive to a clock signal, atest signal and a bit sequence, said arrangement comprising: a memoryunit adapted to store a first time point determined by a duration of atest signal pulse of said test signal; a multiplexer having an inputconnected to an output of said memory unit, and being adapted to switchbetween respective time points allocated to logic values of bits of saidbit sequence and a time point allocated to a duration of a time intervaldetermined by successive clock signal pulses of said clock signal, andhaving an output adapted to provide a selected time point; a counterunit having an output adapted to provide a count value proportional to atime point; a comparator having a comparator output, a first inputconnected to said output of said multiplexer, and a second inputconnected to said output of said counter unit, wherein said comparatoris adapted to compare the selected time point at said output of saidmultiplexer with said count value at said output of said counter unitand to produce a comparator output signal responsive thereto at saidcomparator output of said comparator; and a modulation control unithaving a first input connected to said comparator output of saidcomparator, a second input adapted to receive the clock signal, a thirdinput adapted to receive the bit sequence, a reset output connected andadapted to provide a reset signal to a reset input of said counter unit,and a modulation signal output adapted to provide a modulation signaldependent on said comparator output signal and said bit sequence.